The linear solenoid is an obvious choice for the conversion of electrical to kinetic energy in an austere environment because of its simplicity, comprising primarily a wire wound in a coil. When current is applied, it creates an electromagnetic force on a ferromagnetic shaft or plunger in the center of the coil without the necessity of direct contact: it is action at a distance and thus movement can happen with minimal friction. Additionally, the electrical components are easily isolated from the corrosive effects of the environment.
The downside of the solenoid, the attribute that limits its utility, has to do with the mathematics of a magnetic induction field, in which the force falls off exponentially with the distance. So while the force generated by a 24 V solenoid on its shaft may be relatively high over the first millimeter of displacement, say 10 Newtons, by 2 mm it may fall to 5 N, by 3 mm to 2.5 N, and by 4 mm to 1.25 N, etc.
Accordingly, a continuing search has been directed to the development of a device that provides the simplicity and reliability of solenoids without the exponential decay of force conventionally associated with solenoids.